Many types of internal combustion engines are liquid cooled and use a finned radiator through which hot engine coolant is routed to give up its heat to the atmosphere. And, typically, a rotating fan blows air through the radiator for heat exchange purposes. In a liquid-cooled engine, it is common to drive the fan at engine crankshaft speed. Liquid-cooled engines having radiator-type heat exchangers and fans for flowing air across such heat exchangers are used in such applications as motor vehicles and standby engine-generator sets used to provide standby (emergency) power for facilities such as hospitals, schools and the like.
It is well known that the horsepower available from an internal combustion engine is a function of torque (which, in turn, is a function of engine displacement) and speed. The equation expressing horsepower in terms of torque and speed is well known.
A way to obtain greater horsepower from an engine is to increase its speed and/or its displacement. And given an engine of a particular displacement, higher horsepower can be obtained by running the engine at higher speed. But faster engine speeds are attended by faster fan speeds and, necessarily, higher fan blade tip velocity, even though the increased fan speed is not needed to provide adequate cooling. The result is a noticeably-increased (and objectionable) noise level resulting from the fan.
Earlier workers in the field are not unaware of ways to change fan rotation speed relative to engine speed nor of the fact that high fan speed produces objectionable noise. For example, U.S. Pat. No. 3,763,835 (Miller et al.) discloses an engine cooling fan, the blades of which extend radially to maximum length when the fan is running at slower speed. And at higher fan speed, the blades become shorter because of a centrifugal, weight-actuated camming arrangement. A stated reason for the arrangement is to reduce high speed fan tip noise.
U.S. Pat. No. 2,995,295 (Day) discloses an arrangement for changing fan drive speed as a percentage of engine speed. The pulley concentric with the fan has two pulley members, the relative axial positions of which can be changed to change the effective diameter of the pulley.
In the arrangement disclosed in U.S. Pat. No. 3,872,842 (Medley), both the driving and driven pulleys are capable of having their effective diameters changed. Pneumatic controls are used for the purpose.
While these prior art arrangements have been satisfactory for the intended purpose, they are not without disadvantages. One involves mechanical complexity with seemingly-attendant propensity toward failure. The arrangement of the Miller et al. patent is an example.
Another disadvantage of certain prior art arrangements involves the matter of control of effective pulley diameter. The Medley patent discloses a pneumatic control arrangement which uses valves and temperature sensors to control fan speed.
An improved apparatus for reducing engine fan noise while yet avoiding complexities of certain prior art arrangements would be an important advance in the field of engine cooling.